&#34;rotary piston pump comprising a pump housing and two double bladed rotary pistons&#34;

ABSTRACT

The invention relates to a rotary piston pump comprising a medium inlet, a medium outlet, and two rotary pistons. Each rotary piston has an outer contour with a constant radius R around the axis thereof, in two opposing peripheral regions, respectively over a peripheral angular region α, and, in the other peripheral regions, respectively a continuous contour with radii which are measured from the axis and are shorter than the radius R. The rotary pistons are helicoidal, respectively one front side of each rotary piston being rotated in relation to the other front side by a rotary angle β. The medium inlet and the medium outlet have a rectangular cross-section with two axially parallel edges and two edges extending at right angles to said parallel edges. The angles α and β are measured and adapted to each other in such a way that an imaginary sealing line extending parallel to the respective axis extends over the entire axial length of each rotary piston inside the peripheral region thereof with the other contour and contact radius R.

BACKGROUND OF THE INVENTION

The present invention relates to a rotary piston pump with a pump housing and two two-lobe rotary pistons, wherein the pump housing comprises, on one side, a medium inlet and, on the opposite side, a medium outlet, as well as an internal chamber which, as seen in cross-section, essentially comprises an oval-shaped contour with two mutually opposite semicircles having the radius R, the center points of said semicircles being spaced apart by the distance A, wherein the rotary pistons are pivoted on two parallel axes such that they are rotatable in opposite directions, wherein one of the axes extends through one of the center points of the semicircles and the other one of the axes extends through the other one of the center points of the semicircles, wherein the rotary pistons, while rotating, are each, on the one hand, extending along the housing in a sealing manner in the region of the semicircles and, on the other hand, bearing against the respectively other piston in a sealing manner, wherein, in two diametrically opposite circumferential regions and over a circumferential angular range α, each of the rotary pistons comprises an outside contour with the constant radius R about its axis, wherein each of the rotary pistons comprises, in its remaining circumferential regions, a continuous contour without angle of engagement and without volume containment and with radiuses which, as measured from the axis, are smaller than the radius R, and wherein, as seen in the direction of a connecting line between the two axes, the radiuses of the two rotary pistons, in any position of rotation thereof, add up to form the constant distance A, with formation of an at least linear seal between the two rotary pistons.

A rotary piston pump of the aforementioned type has been disclosed in U.S. Pat. No. 1,361,423 A. This rotary piston pump, which has been primarily conceived as a fire extinguishing pump, possesses a housing which comprises a water reservoir below the internal chamber in which the rotary pistons are rotating. Said water reservoir is in fluid communication with said internal chamber through an inlet that is relatively large in size. As seen in the direction of rotation of the rotary pistons, the edges of the inlet are provided with roundings and transitional bevels, in order to ensure that, while the pistons are rotating, a water volume inside the internal chamber is separated from the water volume contained in the reservoir in a steady manner and with a certain transition phase rather than in an abrupt manner. This is intended to reduce vibrations during operation of the rotary piston pump. Since the inlet is relatively large in size, the size of the outlet must be designed accordingly smaller to ensure that there is still a seal between the inlet side and the outlet side, irrespective of the position of the rotary pistons. This is to disadvantage in that the relatively narrow outlet leads to a high flow resistance for the water delivered by the pump, with the result that the pumping efficiency is reduced. As seen in their axial direction, the rotary pistons used in this rotary piston pump have a linear design.

EP 0 283 755 A1 discloses an apparatus for the distribution of inhomogeneous liquids, and in particular liquid manure. Said apparatus is provided with a distribution element comprising a distribution container for infed liquid with a plurality of outlet openings for discharge lines that can be connected thereto. Therein, the distribution container comprises a housing which is subdivided by partitions, thus forming a plurality of delivery chambers which are separated from each other and are each accommodating one pair of rotary pistons of the Roots rotor type. On their liquid supply side, all of the delivery chambers are in open communication with each other; on their liquid discharge side, they are each provided with a separate outlet. An essential feature of this apparatus is that each separate outlet of the delivery chambers is subdivided in two single outlet ducts which are each assigned to one of the two cooperating rotary pistons of the pair of rotary pistons of the associated delivery chamber. In the rotation mode of the pair of rotary pistons, the two outlet ducts can, through their associated rotating rotary pistons, alternately be separated from and connected to the delivery chamber. This embodiment of the apparatus achieves that the pulsations developing while the rotary pistons are rotating are particularly strong; herein, said strong pulsations are desired in order to deliver the inhomogeneous liquids through said plurality of outlet openings and the discharge lines that can be connected thereto, without occlusions occurring through solids or foreign bodies that are carried along in the liquids. Here as well, the rotary pistons have a linear design, as seen in their axial direction.

A further rotary piston pump is known from EP 0 599 333 A1. In this known rotary piston pump, the radiuses of the rotary pistons at their radially outer ends are each smaller than the radius of the semicircles forming the contour of the housing. At the same time, the center point of the radius of the outer ends of the rotary pistons is, here, offset in outward direction by a radial distance from the axis about which the respective rotary piston is rotatable. As a result, each radially outer end of the rotary pistons just passes the housing along a linear sealing contour when the rotary pistons are set rotating. A disadvantage of this merely linear seal is its high wear and tear, causing the rotary pistons or at least parts thereof to be exchanged relatively often. For that reason, the rotary pistons are designed with exchangeable sealing strips each forming the radially outer part of the rotary pistons and being exchangeable one by one. The exchangeable design of the sealing strips requires relatively intensive construction work, with the result that the price thereof and, thus, of the pump as a whole is increased.

Furthermore, there are known prior art lobe-type pumps, such as disclosed in DE 100 22 097 C1. A characteristic feature of lobe-type pumps are the lobes which, over a relatively large circumferential region, comprise an outside contour the radius of which corresponds to the radius of the semicircles of the housing; in said lobes, the center point of the radius coincides with the axis about which the lobe is rotatable. Furthermore, the lobes of a lobe-type pump are characteristic in that, at its advancing side and at its following side, the radially outer end region of each lobe changes via an acute edge into a concave contour region extending in the direction of the associated rotary axis. During operation of a lobe-type pump, the acute edges are subject to particularly high wear and tear. For that reason, exchangeable edge strips are provided to ensure that nothing but the edge strips have to be exchanged once the acute edges are worn. Here as well, the exchangeable design of the edge strips results in relatively intensive construction work, thus increasing the price of the pump. A lobe-type pump is to further disadvantage in that it is practically not possible to provide the acute edges with a sufficiently durable coating or covering. A third essential disadvantage always exhibited by lobe-type pumps is what is called a cavitation between the concave regions of the two lobes. Said cavitation contains a volume of the medium to be delivered through the lobe-type pump, wherein it is to disadvantage that the contained volume is, in addition, variable. For that reason, a sufficiently large spatial gap must be kept free between the two lobes in order to allow the medium to flow off and flow in the region of the cavitation, particularly if the medium is a non-compressible medium, such as a liquid. For that reason, the acute edges of the lobes are usually chamfered so that the circumference of the lobe vanes is reduced, thus facilitating flowing off of the medium from the cavitation and flowing in of the medium into the cavitation. Herein, however, a reduced performance of the pump must be accepted.

DE 198 02 264 C1 discloses a rotor pump with a pump housing, comprising a pair of rotors which are arranged in said housing and are rotatably driven in opposite directions, wherein said rotors each comprise positive displacement vanes extending in the form of a helical line and at an oblique angle in relation to the associated shaft, wherein, while the rotors are rotating, said positive displacement vanes revolve along the inner side of the wall of the pump housing in a sealing manner while bearing against the respectively other rotor. Said positive displacement vanes that are extending at an oblique angle ensure that pulsations in the medium delivered are reduced, but they bear against the pump housing only along a sealing line. In order to ensure that, despite the oblique extension of the positive displacement vanes and, thus, also despite the oblique extension of the sealing line between said vanes and the pump housing, a seal between the inlet and the outlet of the pump is provided in any position of rotation of the rotors, the contours of said inlet and said outlet must be adjusted accordingly, i.e. reduced in size. Herein, the seal between the positive displacement vanes and the pump housing, which just has the shape of a line, causes high wear and tear which, according to the document cited, is countered by positive displacement vanes comprising an exchangeable sealing strip. The design of the rotors with said exchangeable sealing strips results in increased manufacturing work and, thus to an increased price of the pump as a whole.

As described in EP 0 363 420 B2, a rotary piston pump with helical pistons, furthermore, allows the formation of two mutually opposite edges of said inlet and said outlet such that they extend transversely in relation to the direction of rotation of the rotors and at an oblique angle, in order to adjust the direction of said edges to the oblique extension of the positive displacement vanes which, here, provide a seal against the pump housing along a line only. This results in a contour of said inlet and said outlet each having a trapezoidal or triangular shape. Although this separates said inlet and said outlet from each other in any position of the pistons, this is to disadvantage in that, here as well, the cross-section of said inlet and said outlet is reduced, resulting in an increased flow resistance in both inlet and outlet and, thus, impairing the efficiency of the rotor pump.

SUMMARY OF THE INVENTION

For that reason, the present invention aims at creating a rotary piston pump of the aforementioned type, which obviates the drawbacks disclosed and which allows to achieve a good seal of the rotary pistons against the pump housing and low-pulsation delivery and to prevent cavitations and the gap currents associated therewith. Therein, the rotary piston pump should comprise a good efficiency and low wear and tear, while being cost-effective in manufacture and operation.

This problem is solved by the invention by means of a rotary piston pump of the aforementioned type, which is characterized in that

-   -   the rotary pistons, as seen in their axial direction, are         designed such that they extend along mutually opposite helixes,         wherein one of the front faces of each rotary piston is twisted         in relation to the other front face of the same rotary piston by         a twisting angle β,     -   both the medium inlet and the medium outlet of the pump housing         comprise a cross-section which has, in essence, the shape of a         rectangle with two axis-parallel edges and two edges extending         at right angles thereto, and     -   the circumferential angular range α and the twisting angle β are         each dimensioned and matching each other such that a theoretical         sealing line extending in parallel to the particular axis         extends over the full axial length of each rotary piston within         the latter's circumferential region having the outside contour         with the constant radius R.

The new rotary piston pump according to the invention is to advantage in that it combines a plurality of benefits. Owing to the circumferential region with the constant radius R, a two-dimensional seal is achieved between the rotary pistons and the pump housing, said two-dimensional seal being responsive to wear and tear to an essentially lower degree than a linear seal while, at the same time, producing an improved seal. This ensures prolonged and maintenance-free operation with simultaneously increased efficiency. In the rotary piston pump according to the invention, acute edges that are susceptible to wear and tear are entirely avoided. At the same time, the rotary piston pump according to the invention does not give rise to any cavitations because, owing to the fact that there are no acute edges, angles of engagement will not occur and, thus, any volume of the medium to be delivered by the rotary piston pump is prevented from being contained between the two rotary pistons. For that reason, it is neither necessary to keep free a current gap between the two rotary pistons to allow the medium to flow out of a cavitation or to allow the medium to flow into a cavitation, this in turn being of advantage to the efficiency of the pump and also contributing to low wear and tear of the rotary pistons during operation of the pump. The helical shape of the rotary pistons provides for low-pulsation pump operation, this being of advantage to and even indispensable for a great number of applications and rendering unnecessary pulsation dampers which are often required in other cases. At the same time, both the medium inlet and the medium outlet may have large-size cross-sections which have, thus, a low flow resistance, this also being of advantage to a high pumping efficiency. Since the angles α and β are matching each other as mentioned above, a continuous seal between the suction side and the delivery side of the pump remains ensured in any position of the rotary pistons, due to the latter bearing against the pump housing in a two-dimensionally sealing manner, while undesired return flows of the medium through the space between the rotary pistons and the housing are prevented despite the large-size cross-sections of the inlet and the outlet and despite the helical form of the rotary pistons. The seal between the two rotary pistons is at least linear, with the result that, here, the sealing properties are in no way inferior to the rotary piston or lobe-type pumps which are known as such.

In order to achieve an inlet and outlet cross-section that is as large as possible, it is, furthermore, preferrably provided that a first axis-parallel edge of the medium inlet and the medium outlet is, essentially, each positioned on the level of one of the axes and a second axis-parallel edge of the medium inlet and the medium outlet is, essentially, each positioned on the level of the other one of the axes.

A further measure to achieve an inlet and outlet cross-section that is as large as possible is to preferrably provide that, as seen in axial direction of the rotary pistons, a width of the medium inlet and the medium outlet each extends over 80 to 100 percent of the axial length of either rotary piston.

The extent of the helix of the rotary pistons may be different in various pumps, wherein said extent depends on the particular requirements of the application. It is preferrably provided that the twisting angle β is within a range of up to 60°.

In order to achieve a seal that is as good as possible between the rotating rotary pistons and the pump housing, it is desired that the circumferential region with the constant radius R be as large as possible. At the same time, however, the circumferential region with the constant radius R cannot exceed a specific circumferential angular range α of theoretically 90°. A circumferential angular range α of 90° inevitably results in the undesired acute edges, so that a smaller circumferential angular range α is appropriate. For that reason, a circumferential angular range α from 10° to 60° is preferred for the rotary piston pump according to the invention. If the circumferential angular range α is between 10° and 60° as specified, the desired good seal is, on the one hand, ensured between the rotary pistons and the pump housing and, on the other hand, said circumferential angular range α is, at any rate, still so small that acute edges do not become necessary in the course of the further contour of the rotary pistons. By appropriately adjusting the measure of this circumferential angular range α to the aforementioned twisting angle and to the size and/or position of the medium inlet and outlet, it can be ensured that the desired continuous seal between the inlet side and the outlet side of the pump can be easily achieved by means of the rotary pistons.

Furthermore, it is preferrably provided that the circumferential angular range a of the circumferential region with the constant radius R is at least as large as the twisting angle of the helical rotary pistons. In this manner, it is ensured that a theoretical axis-parallel straight sealing line can be placed over the entire axial length of each rotary piston and that, therein, said theoretical sealing line extends in the circumferential region with the constant radius R over its entire length. In this embodiment, the inlet and the outlet can be to advantage in that their width corresponds to the full axial length of the rotary pistons without the desired continuous seal between the inlet side and the outlet side of the pump getting lost.

To ensure that, on the one hand, the rotary piston pump comprises a good efficiency and, on the other hand, its rotary pistons achieve a “slim” cross-sectional shape with a high mechanical stability, it is, furthermore, preferrably provided that the distance A is 1.3 to 1.7, preferrably 1.5 times as big as the radius R.

A further development of the rotary piston pump according to the invention provides that the rotary pistons, as seen in cross-section, each form in each of their two remaining circumferential regions arranged between the two circumferential regions with the constant radius R a succession of three convex contour regions each, wherein one concave contour region is positioned between every two convex contour regions. This shape of the contour represents a geometrically favorable possibility of achieving the desired continuous shape of the rotary pistons, whereby the desired good seal between the two rotary pistons is achieved reliably, wherein a medium volume is prevented from being contained between the rotary pistons, thus also pre-venting cavitations.

Conventional rotary pistons, which bear against the inner perimeter of the pump housing along a sealing line only, give rise to a highly acute wedge-shaped gap between the inside circumferential surface of the housing and the outside surface of the advancing side of each rotary piston. Solid particles contained in the medium to be delivered get stuck very easily in said acute gap; this results in increased wear and tear or even major damage to both the inside surface of the housing and the outside surface of the rotary pistons. In order to avoid this, the invention proposes that the rotary pistons, as seen in cross-section, comprise at the beginning and at the end of each of their two circumferential regions with the constant radius a transition to the respectively adjacent further circumferential region, said transition having the form of an obtuse-angled edge. Said obtuse-angled edge forms a scraping edge, wherein the advancing side of the rotary piston, with its surface region that is immediately arranged adjacent to the scraping edge, encloses a clearly less acute angle with the inner perimeter of the housing. Owing to their cooperation with the inside circumferential surface of the housing, the scraping edges thus ensure that, for the most part, solid particles in the medium to be delivered remain upstream of the rotary pistons as seen in the direction of rotation of the pistons and are transferred by said rotary pistons without getting stuck between the inner perimeter of the housing and the rotary pistons, thus being prevented from causing damage there.

In a practical further development, it is preferrably provided that the obtuse-angled edge encloses an angle ranging from 140 to 160°, preferrably of approximately 150°. On the one hand, this allows to achieve the desired scraping function of the edge and, on the other hand, an excessively sharp edge that is subject to increased wear and tear is prevented.

Furthermore, the invention proposes that, on their surfaces that come into contact with a medium to be delivered through the rotary piston pump, the rotary pistons are provided with a coating or covering which is resistant to said medium. As regards the rotary piston pump according to the invention, a coating or covering can be applied to the rotary pistons without any difficulty, because the latter do not comprise any acute edges impeding a coating or covering. At the same time, the rotary pistons as such can be made of a material that is not resistant to the medium to be delivered, because said material is protected against an attack from the medium through the coating or covering. This allows use of a lower-priced material, for example cast steel or tool steel in the stead of stainless steel. What is more, this allows regeneration of the rotary piston by applying a new coating and covering and reuse thereof in a rotary piston pump, once said coating or covering is worn. As a result, a substantial part of the rotary piston can be used repeatedly.

Preferrably, the coating or covering is made of rubber. With regard to protecting the rotary piston against attacks from the medium to be delivered, a rubber coating or covering provides excellent properties. Moreover, a rubber coating or covering improves, on the one hand, the seal of the rotary pistons against the pump housing and, on the other hand, the seal of the rotary pistons against each other. As a result, undesired return flows in a direction opposite to the desired direction of delivery of the rotary piston pump are reduced further, leading to an improved efficiency of the pump.

BRIEF DESCRIPTION OF THE DRAWINGS

Below, an exemplary embodiment of the invention will be illustrated by means of a drawing, in which

FIG. 1 is a cross-sectional view and, in part, a front view of a rotary piston pump with two rotary pistons extending along a helix in their axial direction;

FIG. 2 is an enlarged view of the front face of an individual rotary piston;

FIG. 3 is a perspective view of the rotary piston pump with an open, partially broken pump housing;

FIG. 4 a is a partial cross-sectional view of a conventional rotary piston pump;

FIG. 4 b is a partial cross-sectional view of the rotary piston pump according to the invention, for comparison reasons; and

FIG. 5 is a perspective view of one of the rotary pistons of FIG. 3 as a single component.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a rotary piston pump 1 comprising a housing 10 and two two-lobe rotary pistons 2 arranged therein. The pump housing 10 delimits an internal chamber 10′ which, in the example shown in FIG. 1, has an oval-shaped inside contour 12, as seen in cross-section. In the upper and lower parts of FIG. 1, the inside contour 12 is formed by contour sections 12.1 each having the shape of a semicircle, the ends of which that are facing each other are connected to each other through two straight contour sections 12.2.

An inlet 11 through which a medium to be delivered is flowing into the housing 10 of the rotary piston pump 1 in flow direction 28 is arranged concealed in the region of the right-hand straight contour section 12.2. An outlet 11′ through which the medium delivered by the rotary piston pump 1 flows out of the pump housing 10 is provided in the straight contour section 12.2 on the opposite side (to the left in FIG. 1). Both the inlet 11 and the outlet 11′ are each rectangular in cross-section. Therein, the inlet 11 is limited by an upper edge 11.1 and a lower edge 11.2 each extending perpendicularly to the drawing plane as well as by two lateral edges 11.3 extending at right angles thereto and in parallel to the drawing plane. Accordingly, the outlet 11′ is limited by an upper edge 11.1′ and a lower edge 11.2′ each extending perpendicularly to the drawing plane as well as by two lateral edges 11.3′ extending at right angles thereto and in parallel to the drawing plane.

Usually, lines (not illustrated) for supplying the medium are arranged up-stream and downstream of the rotary piston pump 1, as seen in flow direction 28 of the medium.

The two rotary pistons 2 in the internal chamber 10′ of the housing 10 are pivoted such that they are rotatable about two axes 20 extending in parallel to each other and perpendicularly to the drawing plane of FIG. 1. Therein, the two axes 20 are spaced apart from each other by a distance A. Here, the two axes 20 each coincide with the center points of the semicircular contour sections 12.1 of the inside contour 12. Moreover, the upper edges 11.1 and 11.1′ of the inlet 11 and the outlet 11′ are, essentially, positioned on the level of the upper axis 20 while the lower edges 11.2 and 11.2′ of the inlet 11 and the outlet 11′ are, essentially, positioned on the level of the lower axis 20, this resulting in large-size and low-resistance flow cross-sections of the pump 1, both on the inlet side and the outlet side.

As shown further in FIG. 1, each of the rotary pistons 2 is provided with two diametrically opposite circumferential regions 21 the radius R of which, as measured from the axis 20, corresponds to the radius R of the semicircular sections 12.1 of the inside contour 12. As seen in circumferential direction of the rotary pistons 2, these circumferential regions 21 with the constant radius R are each extending over a circumferential angular range α of the associated rotary piston 2 wherein, here, the circumferential angular range α is each about 40°. That means that, in this circumferential region 21, each of the rotary pistons 2, while moving along the section 12.1 during operation of the pump 1, bears against the semicircular section 12.1 of the inside contour 12 of the housing 10, thus forming a two-dimensional seal. As a result, an improved sealing effect and reduced wear and tear of the regions 21 of the rotary pistons 2 are achieved as compared with a seal that is merely linear.

In the remaining circumferential regions 22, which are arranged between the two circumferential regions 21 with the constant radius R, the radiuses, as measured from the associated axis 20, are each smaller than the radius R. Therein, the radiuses are each dimensioned in relation to their position on the perimeter of the rotary pistons 2 such that the radiuses of the two rotary pistons 2, as seen along a connecting line between the two axes 20, add up to form the distance A, while forming a seal 27 that is at least linear.

Therein, the contour of the rotary pistons 2 is continuous both in the circumferential regions 21 with the constant radius R and in the two remaining circumferential regions 22 arranged therebetween, said contour being, in particular, formed without any acute edges, with the result that volume containments or cavitations between the two rotary pistons 2 are prevented in any rotational position in relation to each other. At the same time, however, the at least linear seal 27 between the two rotary pistons 2 is ensured in any rotational position of the two rotary pistons 2 in relation to each other.

In the left-hand section of FIG. 1, where the housing 10 is dashed, a plurality of holes 13 used to connect a rear housing lid (not illustrated) to the housing 10 are visible in the background. Said rear housing lid can, at the same time, also be part of a drive unit which can be used to set the rotary pistons 2 rotating in opposite directions.

A few further holes 13′ used to attach, in a detachable manner, a front housing lid (not illustrated) for closing the housing 10 can be seen in the foreground of FIG. 1. With the rotary pistons 2 being designed accordingly, said design being known as such, said rotary pistons 2 can be removed from the housing 10 and installed in the housing 10 while that side of the housing 10 that is facing the viewer is open, without any further disassembly being necessary.

As can be seen further from FIG. 1, the two rotary pistons 2 are designed as helical pistons. That means that the two rotary pistons 2, as seen in their axial direction, that is perpendicularly to the drawing plane of FIG. 2, are intrinsically twisted in mutually opposite direction. In the exemplary embodiment shown in FIG. 1, the angle of this intrinsic twist of the rotary pistons 2 is about 35°, as seen over the entire axial length of the rotary pistons 2, thus being slightly smaller than the circumferential angular range α of the circumferential regions 21 with the constant radius R, which, in the illustrated instance, is about 40°. As regards its upper limit, the twisting angle is limited to such values which reliably ensure the necessary seal between the pump parts that are moving in relation to each other. By means of the helical pistons 2, the pulsations developing while the medium is delivered through the rotary piston pump 1 in flow direction 28 are reduced, this being of advantage to or of essence for many fields of application of the pump 1.

FIG. 2 is an enlarged view of the front face of an individual helical rotary piston 2 for a rotary piston pump according to FIG. 1. In the position of the rotary piston 2 shown in FIG. 2, said rotary piston 2 has, at each of its extreme upper and lower ends, a circumferential region 21 with a constant radius R, measured from the axis 20 about which the rotary piston 2 is rotatable. In the illustrated instance, each circumferential region 21 with the constant radius R extends over a circumferential angular range α of about 24°.

As seen in circumferential direction of the rotary piston 2, two remaining circumferential regions 22 are arranged between the two circumferential regions 21 with the radius R, wherein the radius in said remaining circumferential regions 22 is becoming smaller and is, at any rate, smaller than the radius R.

The transition from one circumferential region 21 to a neighboring circumferential region 22 is each formed by an obtuse-angled edge 26. The four obtuse-angled edges 26 provided on the rotary piston 2 each enclose an angle β. In the example shown in FIG. 2, the angle β is about 150°. The obtuse-angled edges 26 which, during operation, i.e. during rotation of the rotary piston 2, form the advancing edges assume the function of scraping edges in cooperation with the pump housing which is not shown in FIG. 2. As a result, solid particles contained in the medium to be delivered are, to a large extent, prevented from getting stuck between the outer perimeter of the rotary pistons 2 and the inner perimeter of the pump housing which is not shown in FIG. 2.

Either side of each circumferential region 21 is each followed by a convex region 22.1 where the radius of the rotary piston 2, starting from radius R, is steadily becoming smaller away from the circumferential region 21, as seen in circumferential direction.

Two further convex regions 22.1 where the radius of the rotary piston 2 reaches its minimum are each arranged centrally between the two circumferential regions 21 with the radius R, as seen in circumferential direction.

One concave region 22.2, which is provided as a transitional region, is each arranged between every two convex regions 22.1 of the circumferential contour of the rotary piston 2, said convex regions 22.1 neighboring each other. Here as well, the outside contour of the rotary piston 2 has a continuous shape without any acute edges and without any volume containment or cavitations, when two such rotary pistons 2 according to FIG. 2 are used in a rotary piston pump according to FIG. 1.

In addition, FIG. 2 shows a technical possibility of mounting the rotary piston 2 to a shaft 23 which is rotatable about the axis 20. To achieve this, a piston holding body 24, which is cylindrical in its basic shape, is placed onto the shaft 23 in a non-rotatable manner. At its outer perimeter, said piston holding body 24 carries a spring 24′ that projects in an outward direction.

A piston core 25 comprising a hole whose inside diameter including clearance fit corresponds to the outside diameter of the piston holding body 24 is arranged in the interior region of the rotary piston 2 in a non-rotatable manner. Moreover, the piston core 25 is provided with a groove 25′ at its inner perimeter, said groove 25′ having a recess in a radially outward direction and extending in axial direction and accepting the spring 24′ in the assembled state shown in FIG. 2. As a result, the rotary piston 2 is held on the shaft 23 in a non-rotatable manner and with high position accuracy.

FIG. 3 is a perspective view of the rotary piston pump 1 of FIG. 1, wherein a housing lid is removed and wherein the right-hand half of the housing 10 of the rotary piston pump 1, which faces the viewer, is only indicated by dashed lines, in order to make the two rotary pistons 2 arranged in the housing 10 completely visible. FIG. 3 illustrates the helical design of the rotary pistons 2 in a particularly clear manner. The circumferential regions 21 of the rotary pistons 2, which are in sealing cooperation with the semicircular sections 12.1 of the inside contour 12 of the housing 10, are highlighted by a hatched area in FIG. 3. The remaining circumferential regions 22 the contour of which has already been illustrated by means of FIG. 2 are arranged between the circumferential regions 21. Each transition from one circumferential region 21 to a neighboring circumferential region 22 is formed by an obtuse-angled edge 26. Each of the edges 26 that are advancing in the direction of rotation 29 form a scraping edge which cooperates with the section 12.1 of the inside contour 12 of the housing 10 and, to a large extent, prevents solid particles from getting stuck between the rotary pistons 2 and the inside contour 12 of the housing 10.

The two rotary pistons 2 are rotatable about their axes 20 which extend in parallel to each other, in the sense of the rotary arrows 29, that is in opposite directions, this being achieved by means of a drive that is known as such and is not illustrated here.

To the right in the foreground in the illustrated instance, the housing 10 is provided with its inlet 11 in the dashed area, said inlet 11 comprising a rectangular outline. At its top, the inlet 11 is limited by an upper edge 11.1 and, at its bottom, by a lower edge 11.2. Therein, the upper edge 11.1 is, essentially, extending on the level of the upper axis 20 while the lower edge 11.2 is, essentially, extending on the level of the lower axis 20. Moreover, the inlet 11 is limited by two lateral edges 11.3 which are extending in parallel to each other and perpendicularly to the upper edge 11.1 and the lower edge 11.2.

On the opposite side, that is the side facing away from the viewer, the pump housing 10 is provided with its outlet 11′ which also comprises a rectangular outline. In the illustrated instance, an upper edge limiting the outlet 11′ is concealed by the upper rotary piston 2; at its bottom, the outlet 11′ is limited by a lower edge 11.2′. In addition, the outlet 11′ is limited by two lateral edges 11.3′.

As is shown vividly in FIG. 3, both the inlet 11 and the outlet 11′ have a large clear flow cross-section, with the result that the medium delivered by the rotary piston pump 1 is reliably flowing in and out with low resistance. With their circumferential regions 21 extending over a specific circumferential angular range, the rotary pistons 2 ensure at the same time that, despite the helical form of the rotary pistons 2, there is always a good, complete and, at the same time, wear-resistant seal between the inlet side and the outlet side of the pump 1, irrespective of the particular position of the two rotary pistons 2.

Here, any undesired return flow, as could be occurring along the flow arrow 28′ drawn at the top of FIG. 3 if the seal were lacking, is reliably prevented. Therein, this reliable seal also remains preserved if the inlet 11 and the outlet 11′ comprise a clear height which approximately corresponds to the distance between the two axes 20 of the rotary pistons 2 and comprise a clear width which approximately corresponds to the axial length of the rotary pistons 2; this reliable seal is achieved because the two helical rotary pistons 2 are in sealing cooperation with the inside contour 12 of the housing 10 over a circumferential region 21 extending sufficiently far in the circumferential direction of the rotary pistons 2 rather than only along a line.

As shown in FIG. 3, the rotary pistons 2 can be provided with a coating or covering 3, and in particular with a rubber coating or covering, on their outside surfaces coming into contact with the medium to be delivered through the rotary piston pump 1, in order to prevent the medium delivered from immediately attacking the structural material of the rotary pistons 2. Owing to its elasticity, a rubber coating or covering additionally provides an improved seal both of the rotary pistons 2 against the housing 10 and of the rotary pistons 2 against each other. If worn or damaged, the coating or covering 3 can be exchanged while the remaining rotary piston 2 can still be used.

For the purpose of direct comparison, FIG. 4 a is a schematic and partially cross-sectional view of the upper part of the pump, showing a conventional rotary piston pump and in FIG. 4 b, a rotary piston pump according to the invention. In the illustrated instance, the visible part of the pump housing 10 is that part of the housing that comprises the semicircular section 12.1 of the inside contour 12.

In the illustrated instance, the rotary piston 2 of the conventional pump is a three-lobe rotary piston 2; alternatively, this rotary piston 2 may also be a two-lobe or four-lobe rotary piston. As illustrated in FIG. 4 a, this rotary piston 2, irrespective of the number of its lobes, bears against the section 12.1 of the inside contour 12 of the housing 10 in a sealing manner only with a very narrow, practically only linear region 21 as seen in circumferential direction; in the illustrated instance, said linear region 21 extends over a circumferential angle a of only about 3°. This results in a highly acute and wedge-shaped gap between the circumferential region 22 of the rotary piston 2 and the section 12.1 of the inside contour 12 of the housing 10, here with a gap angle of only about 5°, said gap being formed at that side of the rotary piston 2 that is advancing as seen in the direction of rotation 29 of the rotary piston 2.

In FIG. 4 b, the rotary piston pump is equipped with a rotary piston 2 of the aforementioned type that has already been described by means of FIGS. 1 to 3. This rotary piston 2 bears against the section 12.1 of the inside contour 12 of the housing 10 in a sealing manner over a relatively large angular range α of, here, about 50°, as seen in circumferential direction. In circumferential direction, said region 21 is limited by an obtuse-angled edge 26 on either of its sides; as seen in circumferential direction, the further circumferential region 22 is arranged adjacent to said region 21 on either of the latter's sides. By means of the obtuse-angled edges 26, it is achieved that the gap between that side of the rotary piston 2 that is advancing in the direction of rotation 29 and the semicircular section 12.1 of the inside contour 12 of the housing 10 clearly becomes less acute and forms an essentially larger angle of, here, about 32°. This relatively large angle in front of the edge 26 between the advancing side of the rotary piston 2 on the one hand and the inside contour 12 of the housing 10 on the other hand prevents, to a very large extent, solid particles contained in the medium to be delivered through the pump from getting stuck in a harmful manner. In this manner, it is achieved that, by means of the rotary pistons 2, solid particles are transported through the internal chamber 10′ of the housing 10 of the pump in a considerably harmless manner and without the solid particles causing high wear and tear or even major damage to the rotary pistons 2 and the housing 10.

FIG. 5 is a perspective view of a single rotary piston 2 of the rotary piston pump shown in FIG. 3. The rotary piston 2 according to FIG. 5 is rotatable about its rotational axis 20. The circumferential regions 21 that are pointing upwards and downwards in FIG. 5 have a constant radius R (cf. FIG. 2) and, while the rotary piston pump is in operation, rotate such that they bear against the semicircular sections 12.1 of the inside contour 12 of the housing 10 in a sealing and two-dimensional manner.

As seen in circumferential direction, each circumferential region 21 is limited by an obtuse-angled edge 26 on either of its sides, followed by one of the two remaining circumferential regions 22 of the rotary piston 2 on either side in circumferential direction. As has already been illustrated by means of FIG. 2, the remaining regions 22 are, here as well, each consisting of three convex regions 22.1 and two concave regions 22.2 arranged therebetween.

Here, the intrinsic twist of the rotary piston 2, that is the helical shape thereof, as well as the extension of the circumferential region 21 in circumferential direction of the rotary piston 2 are matching each other such that a sealing line 21′ that is dashed in the illustrated instance and extends in parallel to the rotational axis 20 extends over the full axial length of the rotary piston 2 within the circumferential region 21, as is illustrated at the top of FIG. 5. This ensures that the rotary pistons 2 in the housing of the rotary piston pump always provide for a complete and reliable seal between the inlet and the outlet of the rotary piston pump, even if the inlet and the outlet approximately extend over the full axial length of the rotary pistons 2 and over a height that corresponds to the distance between the two rotational axes 20. In this manner, any undesired return flows of the medium delivered, which reduce the performance of the pump and might occur between the circumferential regions 21 of the rotary pistons 2 and the semicircular sections of the inner perimeter of the pump housing, are reliably prevented, without the inlet and the outlet having to be reduced in width and/or height as compared with conventional rotary piston pumps.

As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.

LIST OF REFERENCE NUMBERS Number Description

-   1 Rotary piston pump -   10 Housing -   10′ Internal chamber of 10 -   11 Inlet -   11.1 Upper edge of 11 -   11.2 Lower edge of 11 -   11.3 Lateral edges of 11 -   11′ Outlet -   11.1 Upper edge of 11 -   11.2′ Lower edge of 11′ -   11.3′ Lateral edges of 11′ -   12 Inside contour -   12.1 Semicircular sections of 12 -   12.2 Straight sections of 12 -   13 Holes for rear lid -   13′ Holes for front lid -   14 Mounting feet -   14′ Hole in 14 -   2 Rotary piston -   20 Axis -   21 Circumferential regions with radius R about 20 -   21′ Line across 21 and in parallel with the rotational axis -   22 Remaining circumferential regions -   22.1 Convex regions in 22 -   22.2 Concave regions in 22 -   23 Shafts for 2 -   24 Piston holding body -   24′ Spring -   25 Piston core -   25′ Groove -   26 Edge between 21 and 22 -   27 Sealing line -   28 Flow direction of medium -   28′ Flow arrow -   29 Rotary arrow -   3 Coating or covering 

1.-12. (canceled)
 13. A rotary piston pump with a pump housing and with two two-lobe rotary pistons, wherein the pump housing comprises, on one side, a medium inlet and, on the opposite side, a medium outlet, as well as an internal chamber which, as seen in cross-section, comprises an oval-shaped contour with two mutually opposite semicircles having a radius R, center points of said semicircles being spaced apart by a distance A, wherein the rotary pistons are pivoted on two parallel axes such that they are rotatable in opposite directions, wherein one of the axes extends through one of the center points of the semicircles and the other one of the axes extends through the other one of the center points of the semicircles, wherein the rotary pistons, while rotating, are each, on the one hand, extending along the housing in a sealing manner in the region of the semicircles and, on the other hand, bearing against the respectively other piston in a sealing manner, wherein, in two diametrically opposite circumferential regions and over a circumferential angular range α, each of the rotary pistons comprises an outside contour with the constant radius R about its axis, wherein each of the rotary pistons comprises, in its remaining circumferential regions, a continuous contour without angle of engagement and without volume containment and with radiuses which, as measured from the axis, are smaller than the radius R, and wherein, as seen in the direction of a connecting line between the two axes, the radiuses of the two rotary pistons, in any position of rotation thereof, add up to form the constant distance A, with formation of an at least linear seal between the two rotary pistons, wherein the rotary pistons, as seen in their axial direction, are formed such that they extend along mutually opposite helixes with two front faces, wherein one of the front faces of each rotary piston is twisted in relation to the other front face of the same rotary piston by a twisting angle β, both the medium inlet and the medium outlet of the pump housing comprise a cross-section which has the shape of a rectangle with two axis-parallel edges and two edges extending at right angles thereto, the circumferential angular range α and the twisting angle β are each dimensioned and matching each other such that a theoretical sealing line extending in parallel to the particular axis extends over the full axial length of each rotary piston within the latter's circumferential region having the outside contour with the constant radius R, the rotary pistons, as seen in cross-section, comprise at the beginning and at the end of each of their two circumferential regions with the constant radius R a transition to the respectively adjacent further circumferential region, said transition having the form of an obtuse-angled edge, and the obtuse-angled edges that are advancing in the direction of rotation of the rotary pistons form a scraping edge which cooperates with a section of the inside contour of the housing.
 14. The rotary piston pump according to claim 13, wherein first axis-parallel edges of the medium inlet and the medium outlet are each positioned on the level of one of the axes and second axis-parallel edges of the medium inlet and the medium outlet are each positioned on the level of the other one of the axes.
 15. The rotary piston pump according to claim 13, wherein, as seen in axial direction of the rotary pistons, a width of the medium inlet and the medium outlet each extend over at least 80 percent of the axial length of either rotary piston.
 16. The rotary piston pump according to claim 13, wherein the twisting angle β is within a range of up to 60°.
 17. The rotary piston pump according to claim 13, wherein the circumferential region with the constant radius R extends over the circumferential angular range α which is between 10° and 60°.
 18. The rotary piston pump according to claim 13, wherein the circumferential angular range α of the circumferential region with the constant radius R is at least as large as the twisting angle β of the helical rotary pistons.
 19. The rotary piston pump according to claim 13, wherein the distance A is 1.3 to 1.7 times as big as the radius R.
 20. The rotary piston pump according to claim 13, wherein the rotary pistons, as seen in cross-section, each form in each of their two remaining circumferential regions arranged between the two circumferential regions with the constant radius R a succession of three convex contour regions each, wherein one concave contour region is positioned between every two convex contour regions.
 21. The rotary piston pump according to claim 13, wherein the obtuse-angled edge encloses an angle ranging from 140 to 160°.
 22. The rotary piston pump according to claim 13, wherein, on their surfaces that come into contact with a medium to be delivered through the rotary piston pump, the rotary pistons are provided with a coating or covering which is resistant to said medium.
 23. The rotary piston pump according to claim 22, wherein the coating or covering is made of rubber.
 24. A rotary piston pump with a pump housing and with two two-lobe rotary pistons, comprising: a medium inlet and a medium outlet formed in the housing, an internal chamber formed in the housing which, as seen in cross-section, comprises an oval-shaped contour with two mutually opposite semicircles having a radius R, center points of the semicircles being spaced apart by a distance A, the rotary pistons being pivoted on two parallel axes, the rotary pistons, while rotating, each extend along the housing in a sealing manner in the region of the semicircles and bear against the respectively other piston in a sealing manner, wherein, in two diametrically opposite circumferential regions and over a circumferential angular range α, each of the rotary pistons comprises an outside contour with the constant radius R about its axis, each of the rotary pistons comprising, in its remaining circumferential regions, a continuous contour without angle of engagement and without volume containment and with radiuses which, as measured from the axis, are smaller than the radius R, the radiuses of the two rotary pistons, as seen in the direction of a connecting line between the two axes, in any position of rotation thereof, add up to form the constant distance A, with formation of a linear seal between the two rotary pistons, the rotary pistons, as seen in their axial direction, are formed such that they extend along mutually opposite helixes with two front faces, wherein one of the front faces of each rotary piston is twisted in relation to the other front face of the same rotary piston by a twisting angle β, both the medium inlet and the medium outlet of the pump housing comprise a cross-section which has the shape of a rectangle with two axis-parallel edges and two edges extending at right angles thereto, the circumferential angular range α and the twisting angle β are each dimensioned and matching each other such that a theoretical sealing line extending in parallel to the particular axis extends over the full axial length of each rotary piston within the latter's circumferential region having the outside contour with the constant radius R, the rotary pistons, as seen in cross-section, comprise at the beginning and at the end of each of their two circumferential regions with the constant radius R a transition to the respectively adjacent further circumferential region, the transition having the form of an obtuse-angled edge, and the obtuse-angled edges that are advancing in the direction of rotation of the rotary pistons form a scraping edge which cooperates with a section of the inside contour of the housing.
 25. The rotary piston pump according to claim 24, wherein first axis-parallel edges of the medium inlet and the medium outlet are each positioned on the level of one of the axes and second axis-parallel edges of the medium inlet and the medium outlet are each positioned on the level of the other one of the axes.
 26. The rotary piston pump according to claim 24, wherein, as seen in axial direction of the rotary pistons, a width of the medium inlet and the medium outlet each extend over at least 80 percent of the axial length of either rotary piston.
 27. The rotary piston pump according to claim 24, wherein the circumferential angular range α of the circumferential region with the constant radius R is at least as large as the twisting angle β of the helical rotary pistons.
 28. The rotary piston pump according to claim 24, wherein the distance A is 1.3 to 1.7 times as big as the radius R.
 29. A rotary piston pump with a pump housing and with two rotary pistons, comprising: a medium inlet and a medium outlet formed in the housing, an internal chamber formed in the housing which, as seen in cross-section, having a contour with two mutually opposite semicircles each with a radius R, center points of the semicircles being spaced apart by a distance A, the rotary pistons being pivoted on two parallel axes, the rotary pistons, while rotating, each extend along the housing in a sealing manner in the region of the semicircles and bear against the respectively other piston in a sealing manner, wherein, in two diametrically opposite circumferential regions and over a circumferential angular range α, each of the rotary pistons comprises an outside contour with the constant radius R about its axis, the radiuses of the two rotary pistons, as seen in the direction of a connecting line between the two axes, in any position of rotation thereof, add up to form the constant distance A, with formation of a linear seal between the two rotary pistons, the rotary pistons, as seen in their axial direction, are formed such that they extend along mutually opposite helixes with two front faces, wherein one of the front faces of each rotary piston is twisted in relation to the other front face of the same rotary piston by a twisting angle β, the circumferential angular range α and the twisting angle β are each dimensioned and matching each other such that a theoretical sealing line extending in parallel to the particular axis extends over the full axial length of each rotary piston within the latter's circumferential region having the outside contour with the constant radius R, the rotary pistons, as seen in cross-section, comprise at the beginning and at the end of each of their two circumferential regions with the constant radius R a transition to the respectively adjacent further circumferential region, the transition having the form of an obtuse-angled edge, and the obtuse-angled edges that are advancing in the direction of rotation of the rotary pistons form a scraping edge which cooperates with a section of the inside contour of the housing.
 30. The rotary piston pump according to claim 29, wherein the twisting angle β is within a range of up to 60°.
 31. The rotary piston pump according to claim 29, wherein the circumferential region with the constant radius R extends over the circumferential angular range α which is between 10° and 60°. 